1. Field of the Invention
The invention relates to soap bars having improved wear rates.
2. The Prior Art
Soap bars which are either transparent or translucent have long been known. There have, however, been several problems associated with such bars. Often, the products are barely translucent. Highly transparent bars are known but these have high rates of wear, especially where the bars are produced by casting methods. Color is a further problem that frequently requires improvement.
One of the first significant reports of clear soap bars is found in U.S. Pat. No. 2,820,768 (Fromont) which first coined the term "neutrogenous" indicating the presence of substantial quantities of acid neutralizing material, i.e. triethanolamine. The compositions of Fromont contain mixtures of 35-40% each of sodium and triethanolammonium soaps and substantial amounts of free triethanolamine. These products, produced by casting, have high rates of wear, are only borderline transparent and have a dark brown color.
U.S. Pat. No. 4,741,854 (Krupa et al.) is also based on triethanolamine casting technology. The patent reports achieving improved color through the use of a combination of sulfur and hydride type reducing agents achieving bars of excellent transparency. The major problem with these bars is, however, that they have a high rate of wear being used up relatively quickly under normal hand washing conditions.
Alternative to the casting technology of Fromont and Krupa et al. is that of high shear working of soap to reduce the size of solid crystals. Size reduction minimizes or even eliminates light scattering by the solid crystals thereby achieving light transmission, i.e. clarity. For instance, U.S. Pat. No. 4,517,107 (Clarke et al.) reports a soap-containing formulation becoming clear through shear working between two mutually displaceable surfaces in an apparatus known as a cavity transfer mixer. While products from this process have excellent wear and are readily manufactured, a translucent rather than a transparent product results.
GB 2 182 383 (Dawson et al.) reports a beta-phase soap which is a mixture of solid soap and water-soluble polymer produced by a milling process. Lather characteristics are said to be much improved by use of the water-soluble polymer with no impairment of clarity. A diverse variety of suitable polymers were disclosed including copolymers derived from acrylic acid and/or methacrylic acid, cationic or nonionic guar gums and copolymers of dimethyldiallyl ammonium chloride/acrylamide and dimethyl aminoethylmethacrylate/acrylamide copolymers. As with all high shear mixing processes, the bars of Dawson et al. although claiming transparency are in fact at best only translucent. Similar types of polymers are incorporated into syndet bars, as reported in U.S. Pat. No. 4,673,525 (Small et al.), to improve skin feel and as a mildness aid.
EP 0 186 148A2 (Nagarajan) provides another report of milled syndet bars thickened with water-swellable or water-soluble homo- and co-polymers incorporating acrylic acid. Improvements in humectancy, lather and cracking are noted. There is no indication given that any of these polymers are particularly suitable for reduction of wear in clear bars, especially those produced through casting.
Accordingly, it is an object of the present invention to provide a soap bar having phase homogeneity and low wear rates.
Another object of the present invention is to provide a soap bar of phase homogeneity and low wear rate that can be produced in a casting process employing a low viscosity soap solution.
These and further objects and advantages will become more apparent in the further description of the present invention.